Plovdiv is about a 6-7 hour bus ride from Istanbul. It is a fairly good size town and has its charm. Actually feels more like a town in the midwest of the United States rather than that of a former eastern block country. I didn't bump into one tourist while here for my 3 days and it seems virtually no one in Bulgaria speaks English.
Favourite spots:
The center square of town. The Russian mafia has moved into this area and it is interesting to watch men in full leather clothing with a beautiful woman in each arm. I enjoyed just sitting back and viewing the ego's of the area. It truly is a different world and worth stopping off in if you happen to pass this way.
To the right is the Bachkov Monestary Church a few miles outside of town. Worth going to and easy to hire a taxi for the amount of time you want to be there. Decide on a price before hand! (naturally)
What's really great:
There are some Roman ruins in the center of town but they are poorly marked and not too exciting to see, however there is a fair amount of them throughout town so it does create an interesting atmosphere.
Accommodations:
Tough. It is more expensive here and I didn't have an L.P. with me so I forked over some money to stay in a nicer place.